System and method for clock modeling in discrete-event simulation

Abstract

Local clock modeling for a discrete event simulator is described. A local clock generator provides realistic clock characteristics in terms of clock precision and clock drift and clock mapping utilities provide API for other modules and/or protocols in the discrete event simulator to schedule events on local clocks instead of global clock of the simulator.

1. A method of discrete element simulation comprising the steps of:
 (a) separating an operation of network elements to be simulated into a plurality of logically separate processes, wherein a first process of the plurality of logically separate processes is a simulation of an event performed by a first network element and wherein a second process of the plurality of logically separate processes is a simulation of an event performed by a second network element, wherein the first network element includes a first local clock that generates a first local time and the second network element includes a second local clock that generates a second local time; 
 (b) selecting at least one clock characteristic for the first local clock that relates a local time generated by the first local clock to a logical time associated with a logical time reference; 
 (c) selecting at least one clock characteristic for the second local clock that relates a local time generated by the second local clock to a logical time associated with the logical time reference; 
 (d) scheduling the first process for execution at a first local time; 
 (e) scheduling the second process for execution at a second local time; 
 (f) converting the first local time to a first logical time associated with the logical time reference; 
 (g) converting the second local time to a second logical time associated with the logical time reference; and 
 (h) simulating the operation of the network elements by executing the first process at the first logical time and the second process at the second logical time. 
 
     
     
       2. The method of  claim 1  wherein selecting at least one clock characteristic for the first local clock and at least one clock characteristic for the second local clock comprises modeling actual operation of the first local clock and the second local clock according to the equation:
     x ( t )= x   0   +y   0   t+ ½ Dt   2 +ξ( t )
 
 where: 
 x(t) is local time 
 x 0  is time offset in seconds 
 y 0 t is frequency offset in part per million (ppm) 
 ½ Dt 2  is frequency drift in ppm/year 
 ξ(t) is random deviation in 10 −8 *sec. 
 
     
     
       3. The method of  claim 2  wherein the parameters x 0 , y 0 , D and ξ are the same for the first and second local clocks. 
     
     
       4. The method of  claim 1  wherein the operation of network elements is at least one of, the operation of wireless transceivers, the operation of communication nodes, the operation of computer nodes, the operation of industrial machinery, and the operation of a network of sensors. 
     
     
       5. The method of  claim 1  wherein the logical time reference is based on the first or second local clock. 
     
     
       6. The method of  claim 1  wherein the logical time reference is based on at least one of a recognized universal time standard and a logical time generated by a discrete element simulator. 
     
     
       7. The method of  claim 6  wherein the recognized universal time standard is a global positioning system (GPS) based reference. 
     
     
       8. A method of discrete event simulation comprising the steps of:
 (a) separating an operation of network elements to be simulated into a plurality of logically separate processes, wherein a first process of the plurality of logically separate processes is a simulation of an event performed by a first network element and wherein a second process of the plurality of logically separate processes is a simulation of an event performed by a second network element, wherein the first network element includes a first local clock that generates a first local time and the second network element includes a second local clock that generates a second local time; 
 (b) scheduling a first logically separate process to be executed at a first logical time with respect to a common logical time reference; 
 (c) scheduling a second logically separate process to be executed at a second logical time with respect to the common logical time reference; 
 (d) executing the first logically separate process at the first logical time; 
 (e) executing the second logically separate process at the second logical time; 
 (f) selecting at least one clock characteristic for the first local clock that relates a local time generated by the first local clock to the common logical time reference; 
 (g) selecting at least one clock characteristic for the second local clock that relates a local time generated by the second local clock to the common logical time reference; 
 (h) identifying the first local time, wherein the first local time is the local time output by the first local clock at the time of execution of the first process; and 
 (i) identifying the second local time, wherein the second local time is the local time output by the second local clock at the time of execution of the second process. 
 
     
     
       9. The method of  claim 8  further comprising the step of mapping the identified execution times of the first and second logically separate processes to the logical time reference. 
     
     
       10. The method of  claim 9  wherein the mapped execution times are used to schedule the first logically separate process using the first local clock. 
     
     
       11. The method of  claim 9  wherein the mapped execution times are used to schedule the first logically separate process using the second local clock. 
     
     
       12. The method of  claim 8  wherein selecting at least one clock characteristic for the first local clock and at least one clock characteristic for the second local clock comprises modeling the first local clock and the second local clock according to the equation:
     x ( t )= x   0   +y   0   t+ ½ Dt   2 +ξ( t )
 
 where: 
 x(t) is local time 
 x 0  is time offset in seconds 
 y 0 t is frequency offset in part per million (ppm) 
 ½ Dt 2  is frequency drift in ppm/year 
 ξ(t) is random deviation in 10 −8 *sec. 
 
     
     
       13. The method of  claim 12 , wherein the parameters x 0 , y 0 , D and ξ are the same for the first and second local clocks. 
     
     
       14. The method of  claim 8  wherein the operation of network elements is at least one of, the operation of wireless transceivers, the operation of communication nodes, the operation of computer nodes, the operation of industrial machinery, and the operation of a network of sensors. 
     
     
       15. The method of  claim 8  wherein the logical time reference is based on a recognized universal time standard. 
     
     
       16. The method of  claim 8  further comprising logging the first local time as the local time output by the first local clock when the first network element performed the first event.